1. Field of the Invention
The present invention relates to generating a tunable DC slope, and a related architecture.
2. Description of the Prior Art
Reference voltages are voltages that follow an external supply voltage. Stable reference voltages are commonly generated by resistor divider circuits. This circuit generates an output voltage that is a fraction of an external supply voltage, but also follows the external voltage closely.
Please refer to FIG. 1. FIG. 1 is a diagram of a typical resistor divider circuit 100. The circuit 100 consists of a first resistor R1 coupled in series with a second resistor R2. R1 is supplied with an external voltage supply Vext and R2 is coupled to ground. The generated voltage Vout is equivalent to the voltage across R2. BY varying the resistance across the two resistors, the size of the output voltage can also be varied. For example, if R1=R2 then the output voltage will be half the supply voltage.
Although resistor divider circuits generate a reference voltage that closely follows the supply, such a close relationship is not always necessary or desired. For example, when a reference voltage is used as a reference for overclocking a circuit, the desired voltage should follow an external voltage at a tunable ratio. Resistor divider circuits are limited in the type of slope they can produce. The gradient of the slope will always be the same as that of the supply voltage gradient, and the intercept is always zero. It is therefore an aim of the present invention to provide a circuit for generating a reference voltage that only has a slight dependence on the supply voltage and can be tuned.